Physics 151 Week 5 Day 2 Topics  Using Motion Models  Pictorial (a.k.a Picture) diagram  Solving Motion Problems using Strategic Problem Solving (SPS) Approach

Problem Solving Strategy (PSS) When solving problems, it is important to show how you reasoned from the information given in the problem and key physics ideas to your final answer. The correct final answer with units is only worth 1-3 points. The remainder of the points (70-90% of credit) are awarded for the quality of your solution. You are expected to include the following to receive full credit: Prepare Identify the Physics: State explicitly which physics’ principle(s) apply to the problem situation and that you will use to solve the problem Drawing a Picture: Draw at least one picture to visualize the physics of the problem and define your variables and constants. For motion problems this could be a motion diagram, motion graph, or pictorial diagram Collecting Necessary Information: State all the information given in the problem with correct units. Include preliminary calculations such as unit conversions Assume/Observe: State assumptions or observations that would be useful Solve Start with key equation(s) in symbol form Solve for the unknown quantity in symbols before numeric calculations Then substitute numbers with units and calculate the numeric answer Assess Check to see if your answer is reasonable Does it answer the question that was asked Does it have the right units?

Pictorial Diagrams

Pictorial Diagram Example 2

Slide 2-34 Hints for Motion Problems 1.Start with a diagram or graph and break the motion into motion intervals 2.Identify the motion models that pertain to each interval. 3.Think about what motion relationships exist in the problem situation. 4.For constant a motion, write out the 3 equations and underline what you know and circle what you are looking for. This can help suggest how to approach the problem. 5.Do your algebra in symbols. It will make problem solving easier.

The Sprinter A sprinter accelerates at 2.5 m/s^2 until reaching his top speed of 15 m/s. He then continues to run at top speed. How long does it take him to run the 100 m dash?

Down and Up A ball is released on the left side at a height of 1 m on a frictionless 30 degree slope, |a| = 5 m/s 2. At the bottom, it turns smoothly onto a 60 degree slope going back up, |a| = 8.66 m/s 2. What maximum height does it reach on the right side?

Timing the light You have a summer job working for the UNM police department studying traffic flow on and near campus. There have been several complaints concerning the signal on Yale and Central Avenue for drivers on Central. The complaints claim that the yellow light is too short. If most cars decelerate at 10.0 m/s 2 while braking, how long should the light be so that people who can ’ t stop before they go into the intersection after the signal turns yellow have time to go through the 16.0 m wide intersection?